OP0256 VALIDATION OF THE 2019 ACR/EULAR CLASSIFICATION CRITERIA FOR IGG4-RELATED DISEASE AND THE JAPANESE ORGAN-SPECIFIC DIAGNOSTIC CRITERIA IN A JAPANESE IGG4-RELATED PERIAORTITIS/RETROPERITONEAL FIBROSIS COHORT: A NATIONWIDE MULTICENTER STUDY
Authors: I. Mizushima, N. Morikage, E. Ito, F. Kasashima, Y. Matsumoto, N. Sawa, H. Yoshifuji, T. Saeki, Y. Domoto, S. Shimada, T. Takayama, E. Amiya, H. Takahashi, M. Kawano, S. Kasashima
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Diagnosing IgG4-related periaortitis/retroperitoneal fibrosis (IgG4-PA/RPF) is often challenging, especially in PA/RPF-limited cases, due to the difficulty in obtaining periaortic/retroperitoneal specimens. In addition to the Japanese diagnostic criteria for IgG4-PA/RPF [1], the 2019 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for IgG4-related disease (IgG4-RD) [2] have not been validated for IgG4-PA/RPF diagnosis in daily clinical practice. <h3>Objectives</h3> This study aimed to validate the ACR/EULAR classification criteria and the Japanese organ-specific diagnostic criteria in a Japanese cohort of patients with IgG4-related PA/RPF. <h3>Methods</h3> In this nationwide multicenter study, we retrospectively reviewed the medical records of 110 patients with IgG4-PA/RPF and 79 non-IgG4-RD patients (mimickers) diagnosed by experts. Using the collected data, we calculated sensitivity and specificity in both the ACR/EULAR classification criteria and the Japanese diagnostic criteria. To clarify the characteristics of false-negative cases of IgG4-PA/RPF, we compared the clinical features between the false-negative and true-positive cases. <h3>Results</h3> Patients with IgG4-PA/RPF and mimickers had a median age of 70 and 71 years, and were 90% and 68% male, respectively. The final diagnoses of mimickers mainly consisted of non-IgG4-related idiopathic PA/RPF, lymphoma, Takayasu arteritis, giant cell arteritis, and atherosclerotic or infectious aortic aneurysm. The ACR/EULAR classification criteria had a sensitivity of 52% and a specificity of 95%. Of the 53 false-negative cases, 13 did not fulfill the entry criteria, 13 fulfilled one exclusion criterion, and 36 did not achieve sufficient inclusion criteria scores. Compared with the true-positive cases, the false-negative cases had significantly lower serum IgG4, IgG, and IgE levels, higher serum C3 and C4 levels, and lower prevalence of extra-vascular/retroperitoneal lesions; frequency of periaortic/retroperitoneal biopsies (36% vs 37%), frequency of storiform fibrosis and obliterative phlebitis in the obtained specimens, and numbers of infiltrating IgG4-positive cells were similar between the false-negative and true-positive cases. The Japanese diagnostic criteria for IgG4-PA/RPF had a sensitivity of 63% and a specificity of 99% when definite and probable diagnoses in the diagnostic criteria were regarded as a diagnosis of IgG4-PA/RPF (a strict version). When definite, probable, and possible diagnoses were regarded as a diagnosis of IgG4-PA/RPF (a lenient version), the diagnostic criteria had a sensitivity of 95% and a specificity of 90%. <h3>Conclusion</h3> The present study suggests that the 2019 ACR/EULAR classification criteria for IgG4-RD and a strict version of the Japanese diagnostic criteria for IgG4-PA/RPF have an excellent diagnostic specificity in daily clinical practice. A lenient version of the Japanese diagnostic criteria serves as more sensitive criteria, although care should be taken to avoid misdiagnoses for mimickers due to the relatively low specificity. <h3>References</h3> [1]Mizushima I, et al. Clinical and pathological characteristics of IgG4-related periaortitis/periarteritis and retroperitoneal fibrosis diagnosed based on experts' diagnosis. Ann Vasc Dis. 2019;12:460-72. [2]Wallace ZS, et al. The 2019 American College of Rheumatology/European League Against Rheumatism classification criteria for IgG4-related disease. Ann Rheum Dis. 2020;79:77-87. <h3>Acknowledgements</h3> We sincerely thank all the members of IgG4-related cardiovascular disease working group. <h3>Disclosure of Interests</h3> None Declared.